The present invention relates to processes for the production of amethyst crystals which find an extensive use in jeweller's art as semi-precious stones.
Known in the art is a process for producing amethyst crystals by growing colourless quartz crystals using a hydrothermal method of a temperature drop in a high-pressure autoclave on crystalline seed plates oriented parallel to crystallographic planes of the major {1011} rhombohedron or the minor {1101} rhombohedron and with the use of silica as a charge; the crystal growth is effected from aqueous solutions of potassium carbonates containing iron introduced into the autoclave in the form of metallic iron; the thus-grown colourless quartz crystals are exposed to an ionizing radiation.
This prior art process for amethyst crystal growing has the following disadvantages:
1. Rather poor reproducibility of the process of growing colourless quartz crystals due to non-specified process parameters, namely crystallization temperature and pressure in the autoclave.
2. Relatively low growing rates (of the order of 0.005 to 0.02 mm/day) of colourless quartz crystals on seed plates of said crystallographic orientations.
3. Insufficient purity of amethyst crystal colour. This may be attributed to the fact that during growing colourless quartz crystals from aqueous solutions of potassium carbonate said crystals intensively entrain aluminium accumulated in such solutions as a result of the charge dissolution. The aluminium forms, in the colourless quartz crystals, potential centers of the smoky colour which after the exposure to an ionizing radiation result in the formation of a smoky tint in amethyst crystals, whereby the value of the amethyst crystals is substantially reduced.
4. Considerable fracturing of the amethyst crystals.